Surface treatment process for coloring metal articles

ABSTRACT

A surface treatment process for coloring metal articles includes following steps. In a first step, a metal article is anodized to form a first anodic oxide layer including a first portion and a second portion on the original metal article. In a second step, the anodized metal article is dyed. In a third step, the first portion of the first anodic oxide layer is removed from the anodized metal article to partially expose a metal body of the anodized metal article. In a fourth step, the exposed metal body of the anodized metal article is anodized to form a second anodic oxide layer. In a fifth step, the exposed metal body of the metal article is dyed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface treatment processes for coloring metal articles.

2. Description of Related Art

Metal articles made of, e.g., aluminum, magnesium, titanium, or alloys thereof, have various mechanical attributes making them popular for a wide range of applications and in many industries such as housings for mobile devices. Metal articles usually undergo surface treatment for improving decorative quality or surface durability.

Anodizing is a surface treatment carried out in an anodizing solution for improving the decorative quality and/or surface durability of the metal articles. During anodization of the metal articles, a porous anodic oxide film is formed over the surface of the metal articles. The anodized metal articles are often subsequently colored to obtain decorative appearances. The coloring of the metal articles can be carried out in a dye solution. However, the color of the paint particles cannot be altered during coloring of the metal articles. Thus only a single-color appearance can be obtained by a combination of the anodizing process and the coloring process. However, consumers desire multi-colored metal articles.

Therefore, a surface treatment process for coloring metal articles is desired.

DETAILED DESCRIPTION OF THE INVENTION

In a present embodiment, a surface treatment process for coloring metal articles may include the following steps.

In a first step, a metal article made of at least one of steel, aluminum, titanium, magnesium, or alloys thereof is provided. Degreased using an alkali-based cleaning solution removes oil stains on the metal article.

In a second step, the metal article is chemically polished to smooth and clear its surface. During the chemical polishing step, the metal article 10 is immersed in a chemical polishing solution typically containing phosphoric acid and sulfuric acid. Chemical-mechanical polishing (CMP) processes are well known.

In a third step, the metal article is processed in a first anodizing process carried out in an electrolyte containing about 180 to 200 g/l (gram per liter) sulphuric acid and metal ions less than about 20 g/l, using a direct current in an approximate range from 11 volts to 13 volts for 30 to 50 minutes. As electrolysis proceeds, a first anodic metal oxide layer grows on the metal article. After anodizing, the surface of the anodized metal article is effectively the first anodic oxide layer on the original metal article.

In a fourth step, the metal article is colored in a first dyeing process. The first dyeing process can be a chemical coloring process.

In a fifth step, the anodized metal article is processed using in a first sealing process to improve anti-contamination performance and anti-corrosion performance of the first anodic oxide layer of the anodized metal article. The first sealing process is carried out, for example in a nickel salt solution, e.g. nickel acetate or nickel fluoride.

In a sixth step, the anodized metal article is coated by a light curable ink to form a light curable coating with a thickness of about 10 to 50 microns. The light curable coating may entirely cover the first anodic oxide layer of the anodized metal article.

In a seventh step, a flexible film is provided. The flexible film includes a transparent portion and a patterned portion. The patterned portion has been exposed and has a light opaque coating formed thereon. The flexible film is applied onto the anodized metal article to cover the light curable coating. A vacuum generator can be employed to draw out the air contained between the flexible film and the anodized metal article, thereby enabling the flexible film to be closely attached to the anodized metal article.

In an eighth step, the anodized metal article is exposed using an exposure machine at exposure energy of about 100 to 150 mj/cm² (micron joule per square centimeters). During exposure of the anodized metal article, one portion of the light curable coating covered by the transparent portion of the flexible film is cured. The other portion of the light curable coating covered by the patterned portion of the flexible film remains uncured.

In a ninth step, the flexible film is removed from the anodized metal article. The anodized metal article is then immersed into a photographic developer to remove the uncured light curable coating. Thus, the first anodic oxide layer has a first portion exposed to the environment and a second portion covered by the cured light curable coating.

In a tenth step, the first portion of the first anodic oxide layer is removed from the anodized metal article by a chemical etching process. During the chemical etching process, the anodized metal article is immersed into a chemical etching solution, e.g., sodium hydroxide solution at a concentration of about 40 g/l, to remove the first portion of the first anodic oxide layer, thereby exposing the metal body of the anodized metal article. The cured light curable coating may protect the second portion of the first anodic oxide layer from being removed. Understandably, a laser etching process can also be employed to remove the first portion of the first anodic oxide layer.

In an eleventh step, the anodized metal article is processed in a second anodizing process. The exposed metal body of the anodized metal article is anodized, thereby forming a second anodic oxide layer on the exposed metal body of the anodized metal article.

In a twelfth step, the metal article is colored in a second dyeing process, to color the surface of the anodized metal article defined by the second anodic oxide layer. The second dyeing process can be a chemical coloring process.

In a thirteenth step, the second anodic oxide layer of the anodized metal article is sealed in a second sealing process that may be carried out in a nickel salt solution, e.g. nickel acetate or nickel fluoride.

In a fourteenth step, the cured light curable coating covering the second portion of the first anodic oxide layer is removed by a release agent. As the metal article is processed in two different dyeing processes (i.e., the first dyeing process and the second dyeing process), a metal article with a surface having two-colors can be obtained.

It should be understood that the steps 6-14 can be repeated, as desired to thereby obtain a metal article having a surface with more than two colors.

It should be also understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A surface treatment process for coloring metal articles, comprising: providing a metal article; anodizing the metal article, thereby forming a first anodic oxide layer on the original metal article; dyeing the anodized metal article; coating the first anodic oxide layer with a light curable ink; attaching a flexible film to the anodized metal article, with the flexible film covering the light curable ink coating, the flexible film having a transparent portion and a patterned portion, the patterned portion being exposed and opaque to light; exposing the metal article to cure the light curable ink coating covered by the transparent portion of flexible film, with the light curable ink coating covered by the patterned portion of flexible film remaining uncured; removing the uncured light curable ink coating, thereby the first anodic oxide layer having a first portion exposed to the environment and a second portion covered by the cured light sensitive coating; removing the first portion of the first anodic oxide layer form the anodized metal article, thereby exposing a metal body of the anodized metal article to the environment; anodizing the exposed metal body; and dyeing the exposed metal body.
 2. The surface treatment process as claimed in claim 1, wherein the metal article is made of a metal selected from the group consisting of aluminum, titanium, magnesium, steel, and any alloy thereof.
 3. The surface treatment process as claimed in claim 1, further comprising pretreatment pre-treating pre-anodized article by degreasing the surface of the metal article and then polishing the surface of the metal article.
 4. The surface treatment process as claimed in claim 1, wherein the anodizing process is carried out in an electrolyte containing about 180 to 200 g/l sulphuric acid and metal ions less than 20 g/l, at a direct current of about 11 volts to 13 volts for 30 to 50 minutes.
 5. The surface treatment process as claimed in claim 1, wherein the thickness of the light curable ink coating is about 10 to 50 microns.
 6. The surface treatment process as claimed in claim 1, wherein during the step of exposing the metal article to cure the light curable ink coating, the anodized metal article is exposed using an exposure machine at exposure energy of about 100 to 150 mj/cm².
 7. The surface treatment process as claimed in claim 1, wherein the step of removing the uncured light curable ink coating is carried out in a photographic developer.
 8. The surface treatment process as claimed in claim 1, wherein the first portion of the first anodic oxide layer is removed from the anodized metal article by a chemical etching process.
 9. The surface treatment process as claimed in claim 8, wherein during the chemical etching process, the anodized metal article is immersed into sodium hydroxide solution at a concentration of about 40 g/l.
 10. The surface treatment process as claimed in claim 1, further comprising a step of removing the cured light curable coating covering the second portion of the first anodic oxide layer by using a release agent.
 11. A surface treatment process for coloring metal articles, comprising steps of: anodizing a metal article, thereby forming a first anodic oxide layer including a first portion and a second portion on the original metal article; dyeing the anodized metal article; removing a portion of the first anodic oxide layer from the anodized metal article to partially expose a portion of the metal body of the anodized metal article; anodizing the exposed metal body of the anodized metal article to form a second anodic oxide layer; and dyeing the exposed metal body of the metal article.
 12. The surface treatment process as claimed in claim 11, further comprising a step of applying a protective ink coating onto the first anodic oxide layer before removing the first portion of the first anodic oxide layer, the protective ink coating covering the second portion of the first anodic oxide layer.
 13. The surface treatment process as claimed in claim 12, wherein the step of applying a protective ink coating comprising: forming a light curable ink coating onto the first anodic oxide layer; attaching a flexible film to the anodized metal article, with the flexible film covering the light curable ink coating, the flexible having a transparent portion and a patterned portion, the patterned portion being exposed and opaque to light; exposing the metal article to cure the light curable ink coating covered by the transparent portion of flexible film, with the light curable ink coating covered by the patterned portion of flexible film remaining uncured; removing the uncured light curable ink coating.
 14. The surface treatment process as claimed in claim 11, wherein the metal article is made of a metal selected from the group consisting of aluminum, titanium, magnesium, steel, and any alloy thereof.
 15. The surface treatment process as claimed in claim 11, further comprising pre-treating the pre-anodized material by degreasing the surface of the metal article and then polishing the surface of the metal article.
 16. The surface treatment process as claimed in claim 13, wherein the thickness of the light curable ink coating is about 10 to 50 microns.
 17. The surface treatment process as claimed in claim 13, wherein the first portion of the first anodic oxide layer is removed from the anodized metal article by a chemical etching process. 